Analysis of signal oscillation patterns

Abstract

A method for identifying and determining the frequency of scattered radiation fringe patterns for applications such as particle or droplet sizing and laser Doppler velocimetery. The method utilizes a series of windowed Fourier transforms performed on an intensity profile of the scattered radiation to locate a segment where a fringe pattern is located on the intensity profile. A standard Fourier transform is then performed on the segment to determine a dominant frequency of the fringe pattern, from which a physical quantity such as diameter or velocity of the particle or droplet may be derived. The method may be utilized with a line or an array sensor to measure the fringe patterns in a spatial domain, or with a point detector to measure the fringe patterns in the time domain.

1. A method for analyzing a fringe or oscillation pattern comprising: performing a plurality of windowed Fourier transform analyses on a plurality of unique subsets of a one-dimensional intensity profile, each of said plurality of windowed Fourier transform analyses being performed on one of said plurality of unique subsets; generating an abscissa-frequency profile; identifying an abscissa parameter segment of said abscissa-frequency profile having a substantially constant frequency greater than zero; performing a standard Fourier transform analysis on said one-dimensional profile across said abscissa parameter segment; identifying a peak frequency from said standard Fourier transform analysis; and deriving a physical quantity from said peak frequency. 
   
   
     2. The method of  claim 1 , wherein generating an abscissa-frequency profile comprises:
 identifying a set of dominant frequencies, one within each of said unique subsets; and 
 generating said abscissa-frequency profile from said set of dominant frequencies. 
 
   
   
     3. The method of  claim 1  wherein said subsets overlap each other in the domain of said abscissa parameter of said abscissa-frequency profile. 
   
   
     4. The method of  claim 1  wherein each of said subsets comprises a continuous portion of said one-dimensional intensity profile. 
   
   
     5. The method of  claim 1  wherein said abscissa parameter is a time parameter. 
   
   
     6. The method of  claim 5  wherein said physical quantity is a velocity. 
   
   
     7. The method of  claim 1  wherein said abscissa parameter is a spatial parameter. 
   
   
     8. The method of  claim 7  wherein said physical quantity is a particle size or a droplet size. 
   
   
     9. The method of  claim 8  wherein a fringe spacing is determined from said peak frequency and said droplet size or particle size is derived from said fringe spacing. 
   
   
     10. The method of  claim 7  further comprising:
 providing an electromagnetic radiation measuring device that measures a plurality of radiation intensities with a matrix of sensors on a sensing plane, said sensing plane being defined by a first axis and a second axis; and 
 scanning said array of sensors in a direction defined by said second axis to obtain said one-dimensional intensity profile. 
 
   
   
     11. A method of analyzing overlapping fringe or oscillation patterns, comprising:
 (a) performing a windowed Fourier transform analysis on a subset of a one-dimensional intensity profile to determine a power-frequency spectrum of said subset; 
 (b) identifying a dominant frequency within said power-frequency spectrum of said subset; 
 (c) repeating steps (a) and (b) for a plurality of unique subsets across said one-dimensional intensity profile to obtain an abscissa-frequency profile; 
 (d) identifying a plurality of abscissa parameter segments of said abscissa-frequency profile having substantially constant dominant frequencies greater than zero; 
 (e) identifying a plurality of peak frequencies, one for each of said abscissa parameter segments; and 
 (f) determining a physical quantity from each of said peak frequencies. 
 
   
   
     12. The method of  claim 11  wherein said dominant frequency is selected from a predetermined range of frequencies. 
   
   
     13. The method of  claim 11  wherein the abscissa parameter of said abscissa parameter segment is a time parameter. 
   
   
     14. The method of  claim 13  wherein said physical quantity is a velocity. 
   
   
     15. The method of  claim 11  wherein the abscissa parameter of said abscissa parameter segment is a spatial parameter. 
   
   
     16. The method of  claim 15  wherein said physical quantity is a particle size or a droplet size.